[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Fw: [avr-gcc-list] Array of pointers to functions revisited...

From: Royce & Sharal Pereira
Subject: Fw: [avr-gcc-list] Array of pointers to functions revisited...
Date: Tue, 20 Jul 2004 00:49:11 +0530

----- Original Message -----
From: "Ned Konz" <address@hidden>
To: <address@hidden>; "Royce & Sharal Pereira" <address@hidden>
Sent: Monday, July 19, 2004 7:04 PM
Subject: Re: [avr-gcc-list] Array of pointers to functions revisited...

On Sunday 18 July 2004 2:52 pm, Royce & Sharal Pereira wrote:
> Now when I looked at the .lss file it wasn't any fun() :)
> The array call_fun had anything but the addresses of fun1, fun2 etc. !!
> In the .lst file I see a '.word pm(fun1)' instead of a '.word fun1'
> etc.(BTW What's this pm ?)
> The second problem is- The line-
> fun= pgm_read_word(call_fun[f_cnt]);
> does not get the desired address correctly. There is a un-necessary 'ld'
> before 'lpm' which destroys the Z reg, so that the fetched address is
> wrong(I assume you will compile my code & see the result).

Why are you all going through all of the pgm_read_word() stuff? Just good old

 avr-gcc -O3 -Wall -Wl,-Map,test.map -g -mtiny-stack -mint8 -mmcu=atmega16 -o
test.elf test.c;
 avr-objdump -h -S  test.elf > test.lst

 R16/17 is call_fun
 R26 is X reg
 R28 is Y reg
 R30 is Z register

#include <inttypes.h>
#include <avr/pgmspace.h>

static void fun1(void) { }
static void fun2(void) { }
static void fun3(void) { }

typedef void (PROGMEM * pFun)(void);

static pFun PROGMEM call_fun [3] = { &fun1, &fun2, &fun3 };

int main(void)
uint8_t i;
for (i = 0; i< 3; i++)
return 0;
Which produces (on avr-gcc 3.4.0) the extremely straightforward:

int main(void)
  9a: cf e5       ldi r28, 0x5F ; 95
  9c: d4 e0       ldi r29, 0x04 ; 4
  9e: de bf       out 0x3e, r29 ; 62
  a0: cd bf       out 0x3d, r28 ; 61
  a2: c2 e0       ldi r28, 0x02 ; 2
  a4: 04 e5       ldi r16, 0x54 ; 84
  a6: 10 e0       ldi r17, 0x00 ; 0
uint8_t i;
for (i = 0; i< 3; i++)
  a8: d8 01       movw r26, r16
  aa: ed 91       ld r30, X+
  ac: fd 91       ld r31, X+
                           ^ ^^
---'LD'? wasnt the array initialised in ROM earlier? An LPM is required here!
---That was the reason for all the pgm_read_word() stuff.
---Normal C is ok if the array was in ram. But getting avr-gcc to fetch from 
ROM requires some

ae: 8d 01       movw r16, r26
  b0: 09 95       icall
  b2: c1 50       subi r28, 0x01 ; 1
  b4: c7 ff       sbrs r28, 7
  b6: f8 cf       rjmp .-16     ; 0xa8
return 0;


reply via email to

[Prev in Thread] Current Thread [Next in Thread]